Ground fault circuit interrupter with reverse wiring protection

ABSTRACT

A new type of ground fault circuit interrupter (GFCI) with reverse wiring protection preferably includes a pair of fixed contact holders, each having a contact at one end; a pair of movable contact holders, each having a fixed end and a movable end, each of the movable ends having a contact; a movable assembly that moves between first and second positions, wherein the first position is a position in which each of the contacts of the fixed contact holders makes contact with one of the contacts of the movable end of one of the movable contact holders, and wherein the second position is a position in which the contacts of the fixed contact holders are separated from the contacts of the movable contact holders; an electromagnetic resetting component, which, when energized, causes the movable assembly to be in the first position; an electromagnetic tripping component, different from the electromagnetic resetting component, which, when energized, causes the movable assembly to be in the second position; and a control circuit, which, upon detection of a fault condition, energizes the electromagnetic tripping component, and which, upon detection of a reset condition, energizes the electromagnetic resetting component.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority of Chinese Patent ApplicationNo. 02131108.0, filed on Oct. 9, 2002, and incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a ground fault circuitinterrupter (GFCI) for load ground-fault protection. More specifically,the invention relates to a GFCI receptacle adopting an electromagnetictripper and providing reverse wiring protection.

[0004] 2. Discussion of Related Art

[0005] Ground fault circuit interrupter (GFCI) devices are designed totrip in response to the detection of a ground fault condition at an ACload. For example, the ground fault condition may result when a personcomes into contact with the line side of the AC load and an earth groundat the same time, a situation that can result in serious injury. TheGFCI device detects this condition by using a sensing transformer todetect an imbalance between the currents flowing in the line and neutralconductors of the AC supply, as will occur when some of the current onthe line side is being diverted to ground. When such an imbalance isdetected, a circuit breaker within the GFCI device is immediatelytripped to an open condition, thereby opening both sides of the AC lineand removing all power from the load.

[0006] A GFCI generally includes a housing, a tripper, a reset button, atest button, a mounting strap with grounding strap and banding screw, apair of movable contact holders with contacts, a pair of fixed contactholders with contacts, and control circuit. Currently, GFCI is widelyused to prevent electric shock and fire caused by ground fault.

[0007] In the past, a GFCI receptacle generally adopted a mechanicalactuator. It limited the performance of such products, especially inthat these GFCIs did not provide reverse wiring protection. In addition,these mechanical GFCIs required high standards in the quality of theparts and assembling work. Examples of mechanical GFCIs include thosedisclosed in U.S. Pat. No. 5,933,063 and U.S. Pat. No. 4,802,052.

[0008] The GFCI shown in U.S. Pat. No. 6,252,407 B1 has reverse wiringprotection, but it is a visual alarm indicator signaling a miswiringcondition to the installer, and if miswired (despite the visual alarmindicator) by connecting the line to the load, the GFCI can still bereset. Under such circumstances, an unknowing user, faced with a GFCIthat has been miswired, may press the reset button, which, in turn, willcause the GFCI to be reset without reverse wiring protection available.And, such a GFCI that has been reset is very easy to trip again inevents like lightning strikes.

[0009] The design of these GFCIs allows two ways of connection: the loadcan pass through the entry ports of the face portion or canalternatively connect through the load binding screws. Consequently, aninstaller or user can still mistakenly connect the line and the load ina reverse direction. When this occurs, without reverse wiringprotection, the GFCI will function just as a common receptacle.

[0010] There is still a need for a GFCI that has the followingcharacteristics to improve the safety features of the receptacles:capability of providing reserve wiring protection; highly responsive;convenient to assemble; and having better functionality.

SUMMARY OF THE INVENTION

[0011] It is an object of the invention to provide a GFCI circuit thathas the above characteristics.

[0012] In general, a preferred embodiment of a ground fault circuitinterrupter (GFCI) according to the invention will comprise a pair offirst contact holders, each having a contact at one end; a pair ofmovable contact holders, each having a fixed end and a movable end, eachof the movable ends having a contact; a movable assembly that movesbetween first and second positions, wherein the first position is aposition in which each of the contacts of the first contact holdersmakes contact with one of the contacts of the movable end of one of themovable contact holders, and wherein the second position is a positionin which the contacts of the first contact holders are separated fromthe contacts of the movable contact holders; an electromagneticresetting component, which, when energized, causes the movable assemblyto be in the first position; an electromagnetic tripping component,different from the electromagnetic resetting component, which, whenenergized, causes the movable assembly to be in the second position; anda control circuit, which, upon detection of a fault condition, energizesthe electromagnetic tripping component, and which, after a reset switchis activated, energizes the electromagnetic resetting component.

[0013] One particular object of an embodiment of the present inventionis to provide a GFCI receptacle with reverse wiring protection thatadopts an electromagnetic tripper and a corresponding control circuit.

[0014] The GFCI receptacle according to an embodiment of the presentinvention comprises an electromagnetic tripper, a rear portion, acentral body, a face portion, a test button, a reset button, anindicator, a mounting strap with a grounding strap and a binding screw,a pair of movable contact holders having one end fixed and the other endable to freely bias, a pair of fixed contact holders mounted on thecentral body, and a control circuit.

[0015] Because the tripper is electromagnetic, the GFCI receptaclecarries out the breaking and making operation through the interaction ofthe relevant electromagnetic force produced by the trip coil (J₁), theclosing coil (J₂) produces, and the permanent magnet. Furthermore, byusing the magnetic force of the permanent magnet to provide theretentivity of the tripper, the operating sensitivity is improved, andthe GFCI is more energy efficient. According to another feature of theinvention, the GFCI is provided with reverse wiring protection in thatthe control circuit is de-energized when the GFCI is miswired byconnecting the line to the load, so that the GFCI receptacle can not bereset.

[0016] A further object of an embodiment of the present invention is toprovide an electromagnetic tripper that is electronically controlled. Insuch an embodiment (for example, the implementation shown in FIG. 10),the tripper comprises a permanent magnet, a coil framework, a trip coil,a closing coil, a plunger, a trip spring, a movable bracket, a balanceframe, and a small spring providing a contact force for the movablecontact holders. When the reset button is depressed, the closing coilwill be energized and will produce an electromagnetic force thatattracts with the magnetic force of the permanent magnet to act on theplunger to overcome the returning force of the trip spring and certainfriction, thereby obtaining the goal that the tripper closes, and themagnetic force of the permanent magnet maintains the tripper in theclosed condition. Because the plunger and the movable bracket arepressed together, the movement of the plunger directly drives themovable bracket to move along the same direction, and the movement ofthe movable bracket activates the balance frame to move. The movement ofthe balance frame lifts the removable contacts against the fixedcontacts through the special shape of the movable contact holder (theremovable contact has a V-shaped groove, and when it is in the trippingstate, the bracket of the balance frame just locates in the V-shapedgroove). When the tripper is in the closed state, the removable contactconnects with the fixed contacts, and the small spring associated withthe balance frame provides a contact force to maintain good contact allalong, thereby maintaining the GFCI receptacle in the normal operatingcondition.

[0017] When the GFCI receptacle of the above embodiment is energized, ifthere occurs a ground fault at the load or there is a factitious faultcurrent, the control circuit will gate a silicon controlled rectifier(SCR) into conduction to energize the trip coil. The trip coil will thenproduce a electromagnetic force in the direction which repels themagnetic force of the permanent magnet. The electromagnetic force andthe returning force of the trip spring act on the plunger, therebymaking the tripper open quickly.

[0018] Still another object of an embodiment of the present invention isto provide a special control circuit which mainly comprises the DCpower, integrated amplification circuit, sensing circuit, trip circuit,reset circuit, and test circuit. In one embodiment of the invention inwhich these objects are satisfied, four diodes form a full-wave bridgerectifier circuit. After the AC is commutated by the rectifier circuit,there will be DC on the output terminal of the rectifier circuit. Thisembodiment includes an integrated amplification circuit, which may be aspecial IC (for example, of the type RV4145A or RV2145). The sensingcircuit may include a sensor that comprises a sensing transformer and aneutral transformer. The AC line and neutral conductors pass through thetransformers. In operation, the sensing transformer serves as adifferential transformer for detecting a current leakage between theline side of the load terminal and an earth ground, while the neutraltransformer detects current leakage between the neutral side of the loadterminal and an earth ground. When an imbalance between the currentsflowing in the line and neutral conductors of the AC supply is detected,a circuit breaker within the GFCI device is immediately tripped to anopen condition, thereby opening both sides of the AC line and removingall power from the load. In the reset control circuit, the reset switchis connected to a silicon controlled rectifier (SCR). When the resetswitch is closed, the SCR will be gated into conduction and will cause aclosing coil connected with the SCR to be energized to thereby reset theGFCI. Simultaneously, a capacitor is connected to the reset switch tokeep the closing coil energized for an instant. In this way, it preventsthe closing coil from being burned out in the event that the currentflowing through the closing coil is too large and the energized time istoo long.

[0019] The power supply of the control circuit is connected to the ACsupply of the GFCI, so when the GFCI is energized, the control circuitis also energized. But, if the GFCI is miswired by connecting the lineto the load, the control circuit is de-energized, and therefore, theGFCI will not be able to be reset, achieving the reverse wiringprotection function. Because the reset of the GFCI is electronicallycontrolled, the operation is more convenient and the action is moresensitive compared to GFCIs using mechanical means.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention will now be described in further detail inconjunction with the accompanying drawings, in which:

[0021]FIG. 1 is a perspective view of a GFCI according to an embodimentof the present invention;

[0022]FIG. 2 is a side view, in longitudinal section, of the GFCI inFIG. 1 showing the relative positions of the assembly in the tripcondition;

[0023]FIG. 3 is a perspective view of the GFCI in FIG. 1 with the faceportion removed, showing the internal configuration of the GFCI of FIG.1;

[0024]FIG. 4 is an exploded, perspective view of the GFCI in FIG. 1;

[0025]FIG. 5 is an exploded view of the electromagnetic tripper of theGFCI in FIG. 1;

[0026]FIG. 6 is a perspective view of the trip actuator and a portion ofthe GFCI in FIG. 1, showing the assembled relation of the trip actuator;

[0027]FIG. 7 is a detailed, sectional, side view of the GFCI in FIG. 1in the trip condition;

[0028]FIG. 8 is another detailed, sectional, side view of the GFCI inFIG. 1 in the trip condition, from a different perspective from FIG. 7;

[0029]FIG. 9 is a detailed, sectional, side view of the GFCI in FIG. 1in the closed condition; and

[0030]FIG. 10 is a schematic diagram of a circuit of the GFCI accordingto an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031]FIG. 1 shows a view of the exterior of a GFCI according to anembodiment of the present invention. The GFCI receptacle has a housingconsisting of a face portion 30, a central body 20 (not shown in FIG. 1,but appearing, for example, in FIG. 2) and a rear portion 10. The faceportion 30 has entry ports 31 for receiving normal or polarized prongsof a male plug of the type normally found at the end of a lamp orappliance cord set (not shown), as well as ground-prong-receivingopenings 32 to accommodate three-wire plugs. The GFCI receptacle alsoincludes a mounting strap 40 for fastening the receptacle to a junctionbox, and the mounting strap 40 has a threaded opening to receive a screw113 for connection to an external ground wire. A test button 50 extendsthrough an opening in the face portion 30 of the housing. The testbutton 50 can be activated to test the operation of thecircuit-interrupting portion disposed in the device. A reset button 60,which forms a part of a reset portion of the device, extends through anopening in the face portion 30 of the housing. The reset button is usedto activate a reset operation, which reestablishes the electricalcontinuity in the open conductive paths. Electrical connections toexisting household electrical wiring are made via binding screws 110 and111, where the binding screw 110 is a line phase connection, and thebinding screw 111 is a load phase connection. It should be noted thattwo additional binding screws (not shown) are located on the oppositeside of the GFCI receptacle. An indicator 114 (generally alight-emitting diode (LED)) extends through the opening of the faceportion 30 of the housing. When the GFCI is normally energized, theindicator is illuminated.

[0032] The GFCI illustrated in FIG. 1 may be rated, for example, at 20A.The present invention also provides other types of GFCI, at variousamperage ratings, and these GFCI receptacles all have twoconfigurations, one without an indicator and the other with anindicator. Both configurations operate under the same principle.Therefore, the description below, while specifically for the rated 20AGFCI with an indicator, the description also applies to the other typesof GFCIs.

[0033] Referring to FIG. 2, the assembled relation of the GFCIreceptacle is shown in the trip condition. All of the subassemblies andcomponent parts are fixed mainly to the housing (consisting of the faceportion 30, the central body 20 and the rear portion 10) of the GFCI. Anelectromagnetic tripper is set into the GFCI receptacle of the presentinvention. A permanent magnet 71 is set into one end of a coil framework70, and covered by a shield cover 72 outside. One end of the shieldcover 72 is abutted against one side of the rear portion 10. Shieldcover 72 may be constructed of metal and may define a path of a magneticfield generated by at least one of the coils. The coil framework ismounted on a circuit board 90 by four binding pins. A circular core ofsensor framework 80 is set into a fixed hole of the circuit board 90,and the sensor framework 80 is also mounted on the circuit board 90 byfour binding pins. The U-shaped portion of the sensor framework 80 isset into a corresponding groove on the central body 20. There is anisolation layer 82 between the sensing transformer 81 and the neutraltransformer 83. The sensing transformer 81 may be composed, for example,of high original magneto-conductivity magnetic alloy flakes andenamel-insulated wire. The neutral transformer 83 may, for example, becomposed of ferrite (high μ value, large temperature modulus) andenamel-insulated wire. A plunger 75 is molded into the side of a movablebracket 79. The elasticity of a trip spring 76 makes one side of themovable bracket 79 abut against the sensor framework 80 in the tripcondition. The upper side of the movable bracket 79 has a central hole,and a small spring 78 is set into it to prop up balance frame 77 and toprovide a contact force for the contacts. Through the interaction of themagnetic force of the permanent magnet 71 and an electromagnetic forcethat the trip coil 74 or the closing coil 73 produces in an energizedcondition, the plunger 75 activates the movable bracket 79 to drive thebalance frame 77 to move back and forth in the U-shaped groove, asshown. Contact strap 61 is molded into the underside of reset button 60.One end of reset spring 62 props up the reset button 60, and the otherend presses onto mounting strap 40. The test button 50 is propped up bytest strap 51. In one embodiment of the GFCI, this arrangement ensuresthat the top surface of the test button 50 is substantially level withthe surface of the face portion 30, until pressed.

[0034] Referring to FIG. 3, a pair of fixed contact holders 100A and100B with contacts 101 are mounted on the central body 20. A mountingstrap 40 with grounding strap 41 and binding screw 113 is set onto thecentral body 20, and the face portion 30 impacts it. One end of a teststrap 51 is set into a corresponding slot on the central body 20, itsoutside abuts against the inside of the fixed contact holder 100B, andthe other end of the test strap 51 can flexibly contact with the testresistor 52 (shown, e.g., in FIG. 4). The contact strap 61, which ismolded into the underside of the reset button 60, can flexibly contactthe binding pins 63 through the action of the reset spring 62, whichprops up the reset button 60, thus, controlling the reset action of thetripper.

[0035]FIGS. 2 and 3 also show the physical relationship among themounting strap 40, the central body 20, and coil framework 70 (includingboth the trip coil 74 and the closing coil 73). In particular, thesefigures show that mounting strap 40 is physically separated from coilframework 70 by central body 20. Central body 20 may be constructed of,for example, an insulating material. Central body 20 may thus beconstructed such that mounting strap 40 does not define a path of amagnetic field generated by either trip coil 74 or closing coil 73,i.e., such that mounting strap 40 is magnetically isolated from tripcoil 74 and closing coil 73.

[0036]FIG. 4 is an exploded view of the GFCI receptacle according to anembodiment of the present invention. As shown, the GFCI receptaclecomprises a rear portion 10, a central body 20, a face portion 30, amounting strap with a grounding strap 41 and a binding screw 113, a pairof movable contact holders 102A and 102B with contacts 103, a pair offixed contact holders 100A and 100B with contacts 101, an actuator, areset mechanism, a test mechanism and a control circuit. The actuatorcomprises a coil framework 70, a permanent magnet 71, a shield cover 72,a closing coil 73, a trip coil 74, a plunger 75, a trip spring 76, abalance frame 77, a small spring 78 providing a contact force, a movablebracket 79, and four binding pins 701. The reset mechanism mainlycomprises a reset button 60 molded with a contact strap 61 (shown inFIG. 3), a reset spring 62, and a reset binding pin 63. The testmechanism mainly comprises a test button 50, a test strap 51, a testresistor 52, a sensor framework 80, a sensing transformer 81, anisolation layer 82, and a neutral transformer 83. In addition, the lineterminal 104 is connected to the line wire by the line binding screw 110associated with the pressure plate 105; the load can also be connectedto the GFCI through the load binding screw 111 and a correspondingpressure plate 105. All subassemblies and component parts are assembledas shown in the drawing. The rear portion and the face portion of thehousing are connected together by four fastening screws 115. The resetbutton 60 extends through the reset opening 33 on the face portion 30 ofthe housing. The test button 50 extends through the test opening 34 onthe face portion 30 of the housing. One of the ends of each of themovable contact holders 102A and 102B passes through the sensorframework 80 and is soldered onto the circuit board 90. The other end ofeach can move freely.

[0037]FIG. 5 is an exploded view of the electromagnetic tripper of FIG.4. Because the plunger 75 is molded onto the movable bracket 79, themovement of the plunger 75 can drive the sliding boards 79A and 79B tomove back and forth in the runners 70A and 70B, respectively. Themovement of the movable bracket 79 drives the balance 77 to move toperform the operation of breaking and making. The assembled relation ofthe electromagnetic tripper is further shown in FIG. 6.

[0038] Referring now to FIGS. 7, 8, and 9, when the trip coil 74 or theclosing coil 73 is energized, it produces a correspondingelectromagnetic force to interact with the magnetic force of thepermanent magnet 71 and acts on the plunger 75. In this manner, theplunger 75 drives the balance frame 77 back and forth. In the tripcondition, when trip coil 74 is energized, the bracket 77A of thebalance frame 77 is just set into the V-shaped groove A of the movablecontact holder 102A, and the bracket 77B of the balance frame 77 is justset into the V-shaped groove B of the movable contact holder 102B, asshown in FIGS. 7 and 8. As a result, the contacts 101 and 103 areseparated from each other.

[0039] On the other hand, when the closing coil 73 is energized, theplunger 75, under the magnetic force drives the balance frame 77 to movesuch that the brackets 77A and 77B on the two sides of the balance frame77 force the movable contact holders to bias. When one end of theplunger 75 is attracted to and pressed against the permanent magnet 71(i.e., when closing coil 73 is energized), the brackets on two sides ofthe balance frame 77 are just located on the plane position of theV-shaped groove, and hold the contacts 103 of the movable contactholders against the contacts 101 of the fixed contact holders, as shownin FIG. 9. The small spring 78 provides a contact force for the contacts103 and 101 to help maintain the contact. The special shape of themovable contact holders 102A and 102B prevents the plunger 75 from beingattracted and closed in the event of improper operation, and also makesthe tripper break quickly.

[0040]FIG. 10 shows a general GFCI circuit of the present invention.Diodes D₁-D₄ form a rectifying circuit, converting the AC input to a DCoutput. The junction of D₁ and D₂ and the junction of D₃ and D₄ form theAC input terminals and are connected to the line of the GFCI. Thejunction of D₂ and D₄ forms one terminal for the DC output, and thisjunction is referred to as the “ground” hereinafter. The junction of D₁and D₃ forms the other terminal of the DC output and connects with theresistor R₄. The other end of R₄ is connected to the capacitor C₅. Theother end of C₅ is then connected to the “ground”. In the exemplary20A-rated GFCI device, an electrical voltage of approximately 26V formedbetween the two ends of C5 serves as a DC voltage for the circuit.

[0041] As discussed above, the exemplary ground fault circuit has asensor, a trip circuit, a test circuit and a reset circuit. The sensorhas a sensing transformer N₁ and a neutral transformer N₂, as shown inFIG. 10. The AC line and the neutral conductors pass through bothtransformers. The two ends of a sensing coil of sensing transformer N₁connect to opposite ends of the capacitor C₀. One end of the sensingcoil of N₁ serially connects to the capacitor C₁, the resistor R₅, andthen the terminal 1 of the IC (which, as discussed below, may include anamplifier circuit), and the other end of the sensing coil of N₁ connectsto the terminal 3 of the IC, forming a transformer-coupled circuit thatreceives differential voltage inputs. The feedback resistor, R₁,connects to the terminal 1 of the IC at one end and to the terminal 7 ofthe IC at the other end. The magnitude of resistance at R₁ determinesthe amplification of the IC, that is, the threshold value for thetripping action of the GFCI.

[0042] The neutral transformer N₂, the capacitor C₂, and the capacitorC₃ form the neutral ground-fault protection circuit. The two ends of thesensing coil of neutral transformer N₂ are connected to opposite ends ofthe capacitor C₂. One end of the sensing coil of N₂ is further connectedto the capacitor C₃ and the other end of the sensing coil of N₂ isconnected to the “ground”. The other end of the capacitor C₃ isconnected to the terminal 7 of the IC.

[0043] Given the above-described apparatus, neutral ground-faultprotection occurs as follows. The transformers N₁ and N₂ form asigmoid-wave oscillator with a transformer-coupled oscillating frequencyof 5 kHz. When neutral ground fault occurs, this oscillator starts tooscillate. When the magnitude of the oscillation reaches the ICthreshold value, then the terminal 5 of the IC delivers a signal,putting the tripper in motion and the GFCI breaks.

[0044] In other words, in operation, the sensing transformer (N₁) servesas a differential transformer for detecting a current leakage betweenthe line side of the load terminal and an earth ground, while theneutral transformer (N₂) detects current leakage between the neutralside of the load terminal and an earth ground. In the absence of aground fault condition, the currents flowing through the conductors willbe equal and opposite, and no net flux will be generated in the core ofthe sensing transformer (N₁). In the event that a connection occursbetween the line side of the load terminal and ground, however, thecurrent flowing through the conductors will no longer precisely canceland a net flux will be generated in the core of the sensing transformer(N₁). When the flux increases beyond a predetermined value, it will giverise to a potential at the output of the sensing transformer (N₁), whichis applied to the inputs 1 and 3 of the IC and trip circuit, sufficientto produce a trip signal on the output terminal 5. If the ground faultcondition results from the neutral side of the load terminal beingconnected to ground, a magnetic path is established between the sensingtransformer (N₁) and the neutral transformer (N₂). When this occurs, apositive feedback loop is created around an operational amplifier withinthe IC and trip circuit, and the resulting oscillations of the amplifier(IC) will likewise give rise to the trip signal on the output terminal5.

[0045] As discussed above, resistor R₁ is utilized as a feedbackresistor for setting the gain of the circuit and, hence, its sensitivityto ground faults. The capacitors C₁ and C₃ provide AC input coupling. Inthe absence of a ground fault condition, no output is produced by theamplifier (IC) and trip circuit on the output terminal 5. Under thesecircumstances, the negative pole of a silicon controlled rectifier (SCR)VD₇ is connected to the ground of the full-wave bridge rectifier formedby D₁-D₄ (described in detail above), and the positive pole of the SCRVD₇ is connected to trip coil J₁ to maintain it in a non-conductingstate. Similarly, the negative pole of an SCR VD₅ is connected to theground of the full-wave bridge rectifier, and the positive pole of theSCR VD₅ is connected to closing coil J₂ to maintain it in anon-conducting state. Since the current drawn by the resistor R₄ andamplifier and trip circuit is not sufficient to operate the trip coil,the plunger remains motionless.

[0046] The occurrence of a ground fault condition causes the amplifierand trip circuit to produce an output on terminal 5 of the IC, which isapplied to the gate terminal of the SCR VD₇, thereby rendering the SCRVD₇ conductive. This produces a short circuit across the outputs of thefull-wave bridge rectifier, thereby providing a low-impedance path forcurrent to flow through the trip coil J₁. The resulting movement of theplunger causes the movable contacts to move to the open position,thereby removing power from the entry ports of the face portion and theload terminals. This ensures that the GFCI receptacle remains in acondition to detect a ground fault condition immediately upon beingreset.

[0047] The reset switch RESET, the resistors R₂ and R₃, the capacitorsC₆ and C₇, the SCR VD₅, the closing coil J₂, and the breaking switch Kform the reset control circuit. One end of the reset switch RESET isconnected to the junction of R₄ and C₅, the other end of the resetswitch RESET is connected to one junction of R₂ and C₆, which areconnected in parallel. The other junction of R₂ and C₆ is connected tothe gate pole of the SCR VD₅, R₃, and C₇. Capacitor C₇ is connectedbetween the gate and cathode of the SCR VD₅ to serve as a filter forpreventing narrow noise pulses from triggering the SCR VD₅. One end ofthe breaking switch K is connected to the line terminal; the other endof K is connected to the load terminal. It is noted that the contactpoint between the breaking switch K and the line terminal corresponds tothe contact 103 of the movable contact holder, and the contact pointbetween the breaking switch K and the load terminal corresponds to thecontact 101 of the fixed contact holder. The power supply of the controlcircuit is connected to the line of the GFCI, so when the GFCI isenergized, the control circuit of the GFCI is also energized. When thereset switch RESET is closed, the capacitor C₆ is charged up, generatinga trigger signal of about 20˜40 ms to gate the SCR VD₅ into conduction.Consequently the closing coil 73 is energized for a duration of about20˜40 ms. That is, the closing coil 73 produces an electromagnetic forcefor about 20˜40 ms to act on the plunger 75, sufficient to reset theGFCI.

[0048] The IC may be a special integrated circuit, for example, of typeRV4145A or RV2145.

[0049] As discussed above, capacitor C₄ is connected between the gateand cathode of the SCR VD₇ to serve as a filter for preventing narrownoise pulses from triggering the SCR VD₇. For additional protectivepurposes, the circuit shown in FIG. 10 also includes a metal oxidevaristor (MOV) connected across the input terminals of the AC powersource, in order to protect the whole control circuit from transientvoltage surges.

[0050] The test switch TEST and the current limiting resistor R₀ formthe test circuit. The current limiting resistor Ro is connected to thepower source, and the other end of resistor R₀ is connected to the testswitch. The other end of the test switch TEST is connected to the otherend of the load. The test circuit constantly provides the GFCI a 8 mAfault current for periodically checking of the working status of theGFCI. When the test switch is momentarily depressed, sufficient currentwill flow through the resistor R₀ to cause an imbalance in the currentflowing through the sensing transformers. This will simulate a groundfault condition, causing the amplifier and trip circuit to produce anoutput signal on the output terminal 5 that gates the SCR VD₇ intoconduction and thereby momentarily energizes the trip coil. Theresulting movement of the plunger causes the contacts to open, as willoccur during an actual ground fault condition.

[0051] Simultaneously, the GFCI receptacle also provides an indicationcircuit, where a current limiting resistor R6 is connected in serieswith a light-emitting diode (LED) VD₆, and they are connected directlyto the terminals of the load. When the reset button is depressed and theGFCI receptacle is energized, the LED is illuminated. This affords avisual indication to the installer and the user that the GFCI receptacleis in the normal conduction.

[0052] If the GFCI receptacle is inadvertently miswired by connectingthe line to the load, before the breaking switch K closes, the controlcircuit is de-energized. Because the GFCI utilizes an electro-controlledmeans for reset, when the control circuit is de-energized the closingcoil can not be energized. In this manner, the closing coil can notproduce a corresponding electromagnetic force to act on the plunger,thereby keeping the GFCI also de-energized, achieving the reverse wiringprotection function.

[0053] In summary, the present invention provides a GFCI receptacle thatutilizes an electromagnetic tripper and an electro-controlled means tocontrol reset. This GFCI receptacle has reverse wiring protectionfunction and the advantages of tripping rapidly, operating conveniently,and reasonable configuration.

[0054] While only the fundamental features of the present invention havebeen shown and described, it will be understood that variousmodifications and substitutions and changes of the form and details ofthe device described and illustrated and in its operation may be made bythose skilled in the art, without departing from the spirit of theinvention.

We claim:
 1. A ground fault circuit interrupter (GFCI), comprising: apair of fixed contact holders, each having a fixed contact at one end; apair of movable contact holders, each having a fixed end and a movableend, each of the movable ends having a movable contact arranged forcontacting a respective one of the fixed contacts; a movable assemblythat moves between a first position in which each fixed contact makescontact with the respective movable contact and a second position inwhich the fixed contacts are separated from the movable contacts; anelectromagnetic resetting component, which, when energized, causes themovable assembly to be in the first position; an electromagnetictripping component, different from the electromagnetic resettingcomponent, which, when energized, causes the movable assembly to be inthe second position; and a control circuit, which, upon detection of afault condition, energizes the electromagnetic tripping component, andwhich is responsive to a reset condition for energizing theelectromagnetic resetting component.
 2. The GFCI as claimed in claim 1,further comprising: a permanent magnet disposed to act on the movableassembly to at least one of (a) urge the movable assembly toward and (b)maintain it in the first position.
 3. The GFCI as claimed in claim 2,wherein: the electromagnetic tripping means, when energized, produces amagnetic field causing the movable assembly to be repelled from thepermanent magnet; and the electromagnetic resetting means, whenenergized, produces a magnetic field causing the movable assembly to beattracted to the permanent magnet.
 4. The GFCI as claimed in claim 1,wherein the movable assembly comprises: a plunger partially disposedwithin the electromagnetic reset and tripping components and being ableto move back and forth under magnetic force; a sub-assembly connected toand driven by the plunger disposed to move along an axial line of theelectromagnetic resetting and tripping components between the firstposition and the second position.
 5. The GFCI as claimed in claim 3,wherein the sub-assembly comprises: a movable bracket coupled to theplunger; a balance frame disposed on the movable bracket; and a springdisposed between the movable bracket and the balance frame to exertpressure in a direction that tends to separate the balance frame fromthe movable bracket.
 6. The GFCI as claimed in claim 5, wherein thebalance frame is shaped such that when the movable assembly is in thefirst position, the balance frame exerts pressure on the pair of movablecontact holders to cause the movable contacts to make and maintaincontact with the fixed contacts of the fixed contact holders.
 7. TheGFCI as claimed in claim 6, wherein each of the pair of movable contactholders includes a bent section such that when the movable assembly isin the second position, the balance frame fits into the bent section anddoes not exert pressure on the pair of movable contact holders.
 8. TheGFCI as claimed in claim 1, further comprising: an electromagneticsub-housing for containing the electromagnetic tripping and resettingcomponents and for guiding the movable assembly to move between thefirst and second positions along an axis passing through theelectromagnetic tripping and resetting components.
 9. The GFCI asclaimed in claim 1, wherein the control circuit is arranged such thatthe electromagnetic tripping component and the electromagnetic resettingcomponent are not simultaneously energized.
 10. The GFCI as claimed inclaim 1, wherein the control circuit comprises: a sensor component fordetermining the presence of a fault condition and controllingenergization of the electromagnetic tripping component upon detection ofa fault condition.
 11. The GFCI as claimed in claim 10, wherein thesensor component comprises: a pair of coils arranged to measure currentleakage from a line side of a load terminal of the GFCI and from aneutral side of the load terminal of the GFCI, respectively; and anintegrated circuit receiving signals from the coils and generating acontrol signal to cause the electromagnetic tripping means to becomeenergized upon detection that current leakage from at least one of theline side of the GFCI and the load side of the GFCI exceeds apredetermined level.
 12. The GFCI as claimed in claim 11, wherein thepair of movable contact holders pass in parallel through both of thepair of coils.
 13. The GFCI as claimed in claim 1, further comprising: areset mechanism electrically connected to the control circuit; andwherein the control circuit comprises reset circuitry including: circuitmeans for generating a control signal that causes energization of theelectromagnetic resetting component when the reset mechanism has beenactivated.
 14. The GFCI as claimed in claim 1, further comprising: atest mechanism electrically connected to the control circuit; andwherein the control circuit comprises test circuitry that simulates aground fault condition when the test mechanism has been activated, whichcauses the generation of a control signal that causes energization ofthe electromagnetic tripping component.
 15. The GFCI as claimed in claim1, wherein the control circuit comprises: a rectifying circuit forconverting input AC line power to internal DC power for providing DCpower to energize the electromagnetic tripping and resetting means andfor acting as a DC power supply to the control circuit, the rectifyingcircuit being coupled to the rest of the control circuit such that if amiswiring of the GFCI occurs, the control circuit will be de-energized,and the electromagnetic resetting component will not be energized. 16.The GFCI as claimed in claim 15, wherein the movable assembly furthercomprises: spring means arranged to bias the movable assembly toward thesecond position, such that when the electromagnetic resetting means isnot energized, the movable assembly remains in the second position. 17.The GFCI as claimed in claim 1, wherein the control circuit comprises: apair of silicon controlled rectifiers (SCRs), one of which controlsenergization of the electromagnetic tripping component, and the other ofwhich controls energization of the electromagnetic resetting component.18. The GFCI as claimed in claim 1, further comprising: a strap formounting the GFCI and for providing grounding connections; and a housingcomprising: a face portion that covers the strap; a central body; and arear portion in which the electromagnetic tripping component and theelectromagnetic resetting component are housed.
 19. The GFCI as claimedin claim 18, wherein the central body magnetically isolates theelectromagnetic tripping and resetting components from the strap.